Bimetallic strips for energy harvesting, actuation and sensing

ABSTRACT

Disclosed are bimetallic strips that incorporate magnetostrictive materials to enhance and provide sensing, actuating and energy harvesting functions. The bimetallic strips include a positive magnetostrictive Fe-based alloy layer and a flexible layer. The flexible layer may be a negative magnetostrictive layer or a permanent magnet layer. One or more permanent magnet materials may also be used in the arrangement. The bimetallic strips are inexpensive and easily manufactured, and have characteristics that enhance sensing and actuator applications, and enables energy harvesting.

CROSS-REFERENCE TO RELATED APPLICATIONS

This is a continuation of U.S. patent application Ser. No. 12/006,756,filed Dec. 19, 2007, now U.S. Pat. No. 7,834,490, which claims thebenefit of U.S. Provisional Application No. 60/882,259, filed Dec. 28,2006, each of which is hereby incorporated by reference.

STATEMENT OF GOVERNMENT INTEREST

The following description was made in the performance of official dutiesby employees of the Department of the Navy, and, thus the claimedinvention may be manufactured, used, licensed by or for the UnitedStates Government for governmental purposes without the payment of anyroyalties thereon.

TECHNICAL FIELD

The following description relates generally to bimetallic strips, moreparticularly, bimetallic strips that incorporate magnetostrictivematerials to enhance and provide sensing, actuating and energyharvesting functions.

BACKGROUND

Bimetallic strips have been extensively used for numerous applicationsin the past. Such applications include electrical/mechanical actuationand temperature sensing. Typically, bimetallic strips consist of twostrips of different metals that have different expansion and heatingcharacteristics. Consequently, when heated, the strips expand atdifferent rates. Typically, the strips are adjacently attached alongtheir length. Because of the different expansion and heatingcharacteristics, one strip bends over the other when heated, so that thebimetallic strip bends in a predictable manner. When cooled, thebimetallic strip bends in the opposite direction.

Because of the above-recited properties, bimetallic strips are used assensors and actuators. As a sensor, a bimetallic strip can be used todetect changes in temperature, heat, or other environmental conditions.As an actuator, a bimetallic strip may for example, push a switch as itmoves, thereby changing the state of a system. In some applications, abimetallic strip may be provided in a linear form, and in others incurved or coiled form. Generally, bimetallic strips usually comprisematerials such as steel and copper. However, it is desirable to havebimetallic strips that are easy to manufacture and are functional in agreater number of working environments.

SUMMARY

In one aspect, the invention is a bimetallic strip. In this aspect, thebimetallic strip includes a first substantially flat layer. According tothe invention, the first substantially flat layer includes a positivemagnetostrictive material. The bimetallic strip also has a secondsubstantially flat layer attached to the first substantially flat layerforming a dual layered strip. The second substantially flat layer has aflexible material.

In another aspect, the invention is a method of energy harvesting. Themethod includes the providing of a bimetallic strip having a first endand a second end. The bimetallic strip further includes a firstsubstantially flat layer having a positive magnetostrictive material.According to the method, the magnetostrictive material is an Fe-basedalloy having, Fe_(100-x)Al_(x) wherein x is from about 5 to about 25, orFe_(100-y)Ga_(y) wherein y is from about 5 to about 35. Themagnetostrictive material may also be formed of a combination of theFe_(100-x)Al_(x) and the Fe_(100-y)Ga_(y). The providing of thebimetallic strip further includes providing a second substantially flatlayer attached to the first substantially flat layer forming a duallayered strip. According to the method, the second substantially flatlayer has a permanent magnet or a negative magnetostrictive material.The method further includes the attaching of the first end of thebimetallic strip to a first surface, and the attaching the second end ofthe bimetallic strip to an inertial mass or to a second surface. In thisaspect, the method also includes the initiating of a changing magneticarrangement and accompanying changing magnetic flux in the bimetallicstrip by vibrating the first surface to produce a mechanical stress inthe bimetallic strip. The method also includes the inducing of an ACvoltage from the changing magnetic flux in a coil. This is done bywrapping the coil around the outer surface of the bimetallic strip. Theassociated induced current is stored or converted into a desired outputform.

BRIEF DESCRIPTION OF THE DRAWINGS

Other features will be apparent from the description, the drawings, andthe claims.

FIG. 1A is a schematic illustration of a bimetallic strip according toan embodiment of the invention;

FIG. 1B is a schematic illustration of a bimetallic strip according toan embodiment of the invention;

FIG. 2A is a schematic illustration of a bimetallic strip according toan embodiment of the invention;

FIG. 2B is a schematic illustration of a bimetallic strip according toan embodiment of the invention;

FIG. 2C is a schematic illustration of a bimetallic strip according toan embodiment of the invention;

FIG. 3A is method of harvesting energy according to an embodiment of theinvention;

FIG. 3B is a schematic illustration of an energy harvesting arrangementaccording to an embodiment of the invention; and

FIG. 3C is a schematic illustration of an energy harvesting arrangementaccording to an embodiment of the invention.

DETAILED DESCRIPTION

FIG. 1A is a schematic illustration of a bimetallic strip 100 accordingto an embodiment of the invention. As shown, the bimetallic strip 100 isa two-layer structure having a first substantially flat layer 110attached to a second substantially flat layer 120. In this embodiment,the first layer 110 is a metallic strip having positive magnetostrictiveproperties. The first layer 110 may be an alloy of aluminum (Al) andiron (Fe), preferably Fe_(100-x)Al_(x), wherein x is from about 5 toabout 25. The first layer 110 may also be an alloy of gallium (Ga),preferably Fe_(100-y)Ga_(y), wherein y is from about 5 to about 35.Alternatively, the first layer 110 may be a combination ofFe_(100-x)Al_(x), wherein x is from about 5 to about 25, andFe_(100-y)Ga_(y), wherein y is from about 5 to about 35.

To maximize the performance of the bimetallic strips in operations suchas energy harvesting, actuating, and sensing, alloys having substantialamounts of the above outlined Fe-based Ga and Al alloys may also beused. As such, each of the above outlined Fe-based alloy layers, mayoptionally include one or more elements as small additions, such ascarbon (C), manganese (Mn), sulfur (S), beryllium (Be), or Tin (Sn).Thus, for example, layer 110 may be a combination of Fe_(100-x)Al_(x)wherein x is from about 5 to about 25, carbon, and tin. In anotherexample, layer 110 may be a combination of Fe_(100-y)Ga_(y) wherein y isfrom about 5 to about 35, and carbon. In yet another example, layer 110may be a combination of Fe_(100-x)Al_(x), wherein x is from about 5 toabout 25, and Fe_(100-y)Ga_(y), wherein y is from about 5 to about 35,carbon, and tin. It should be noted that the above outlined Fe-basedalloys for layer 110 are merely examples, and other combinations may beused.

The above outlined alloys have desirable properties such as strength,durability, and the ability to be welded. Additionally, the Fe—Al andFe—Ga based alloys have high magnetostrictive levels that are onlyweakly dependent on temperature. The manufacture of the above mentionedFe-based alloys can be readily accomplished because the alloys can betrained by stress annealing and/or magnetic field annealing, and can beinexpensively prepared.

In this embodiment, the second substantially flat layer 120 is aflexible layer. In this embodiment, layer 120 is an alloy havingnegative magnetostrictive properties. The second layer may be nickel(Ni) or an appropriate Ni alloy, or any other alloy having negativemagnetostrictive properties. Ni possesses a magnetostriction of about 50ppm (negative). Consequently, when the second substantially flat layer120 is Ni, the magnetostriction of the first Fe-based layer 110 can bereadily magnetiostrictively matched to that of Ni by adjusting theamounts of Al or Ga. The bimetallic strip 100 composed of the twomagnetostrictively active layers 110 and 120, of the materials outlinedabove would be inexpensive. The Fe alloy as well as the Ni alloy may beprepared from bar stock, rolled stock, or by melt spinning techniques.The first and second layers 110 and 120 may be joined by means ofwelding, brazing, soldering, or any other means of adhesion. AlthoughFIG. 1A shows the bimetallic strip 100 being substantially rectangular,the strip may have any shape associated with bimetallic strips ingeneral. It should be noted that the size and the dimensions of thebimetallic strip and its components may vary depending on theapplication.

FIG. 1B is a schematic illustration of a bimetallic strip 150 accordingto an embodiment of the invention. In this embodiment, the bimetallicstrip generally does not require a magnetic bias field to operateproperly. As shown in FIG. 1B, the bimetallic strip 150 is a two-layerstructure having a first substantially flat layer 110 attached to asecond substantially flat layer 160. In this embodiment, the first layer110 is a metallic strip having positive magnetostrictive properties, asdescribed with respect to the embodiment of FIG. 1A. Thus, as outlinedabove, the first layer 110 may be Fe_(100-x)Al_(x), wherein x is fromabout 5 to about 25, or Fe_(100-y)Ga_(y), wherein y is from about 5 toabout 35, or a combination thereof. With respect to theFe_(100-y)Ga_(y), an alloy with a very large magnetostriction of about400 ppm may be employed. As outlined above, each of the above outlinedFe-based alloy layers, may optionally include one or more additionalelements, such as for example, carbon (C), manganese (Mn), sulfur (S),beryllium (Be), or Tin (Sn).

The second layer 160 shown in FIG. 1B is a flexible material. In thisembodiment, layer 160 is a permanent magnet material. The permanentmagnet material is not required to be particularly magnetically strongbecause fields are only required to be less than about 300 Oe. Thepermanent magnet material of layer 160 provides the proper bias fieldfor the magnetostrictive Fe-based alloy. The permanent magnet may be along thin Alnico magnet material or alternatively a thin coat of commonferrite material in a rubber-like matrix. As with the embodiment of FIG.1A, the first and second layers 110 and 160 may be joined by means ofwelding, brazing, soldering, or any other means of adhesion. AlthoughFIG. 1B shows the bimetallic strip 100 being substantially rectangular,the strip may have any shape associated with bimetallic strips ingeneral. Additionally, the size and the dimensions of the strip and itscomponents may vary depending on the application.

FIGS. 2A, 2B, and 2C show bimetallic strips according to otherembodiments of the invention. FIGS. 2A, 2B, and 2C show bimetallicstrips 200, 250, and 275 respectively, each having three or more layers.Each bimetallic strip is composed of the two strips (elements) of FIG.1A, and one or more permanent magnetic strips. FIG. 2A shows a threelayer bimetallic strip 200 in which a permanent magnet material layer140 is added to the bimetallic strip arrangement (110, 120) of FIG. 1A.Although, FIG. 2A shows the permanent magnet material layer attached tothe Fe-based alloy 110, the permanent magnet material may alternativelyattached to layer 120, thereby sandwiching the negative magnetostrictivelayer 120 between layers 110 and 140. FIG. 2B shows a four layerbimetallic strip 250 in which permanent magnet material layers 140sandwich the bimetallic strip arrangement (110, 120) of FIG. 1A. FIG. 2Cshows a three layer bimetallic strip 275 in which a permanent magnetmaterial layer is positioned between the Fe-based alloy layer 110, andthe negative magnetostrictive layer 120. In each bimetallic strip (200,250, 275), the alloys can be trained by stress and or magnetic fieldannealing to obtain the best magnetic domain configuration to maximizeenergy transfer. Additionally, as stated above, although FIGS. 2A, 2B,and 2C show the bimetallic strips being substantially rectangular, thestrip may have any shape associated with bimetallic strips in general.Additionally, the size and the dimensions of the strips and theircomponents may vary depending on the application.

FIGS. 3A, 3B, and 3C illustrate a method 300 of harvesting energyaccording to an embodiment of the invention. FIG. 3A shows a flowchartof the method 300, and FIGS. 3B and 3C schematically show thearrangement of elements of the energy harvesting method. Step 310 is theproviding of a bimetallic strip 301 having a first end 302 and a secondend 303. According to the method 300, the bimetallic strip 301 may havea structure according to any of the embodiments as outlined with respectto FIGS. 1A, 1B, 2A, 2B, and 2C. For example, if bimetallic strip 301has a structure as outlined with respect to FIG. 1A, then the strip hasa first substantially flat layer that may be Fe_(100-x)Al_(x) wherein xis from about 5 to about 25, or Fe_(100-y)Ga_(y) wherein y is from about5 to about 35, or a combination thereof. As outlined above, each of theabove outlined Fe-based alloy layers may optionally include one or moreadditional elements, such as carbon (C), manganese (Mn), sulfur (S),beryllium (Be), or Tin (Sn). The strip would also have a secondsubstantially flat layer that has negative magnetostrictive properties.The second layer may be nickel (Ni) or an appropriate Ni alloy, or anyother alloy having negative magnetostrictive properties.

Step 320 is the attaching of the first end 302 of the bimetallic strip301 to a first surface 365. The first surface is a surface that ispositioned within a vibration rich environment. For example, the firstsurface 365 may exist in an aircraft or automotive environment. Thefirst surface 365 may also be associated with a common householdappliance, such as a refrigerator, a washing machine, microwave oven.The surface may also, for example, be associated with industrialequipment, buildings, or bridges.

Step 330 is the attaching of the second end 303 of the bimetallic strip301 to a second surface 366. The second surface may also be a surfacelocated within a vibration rich environment. At step 330, the second end303 may also be attached to an inertial mass 367. Any known bonding ormeans of adhesive may be used to attach the strips to the respectivesurfaces and/or mass.

Step 340 is the initiating of a changing magnetic arrangement andaccompanying changing magnetic flux in the bimetallic strip 301. This isaccomplished by vibrating the first surface to produce a mechanicalstress in the bimetallic strip. FIGS. 3B and 3C show the first surfacevibrating in direction 380. However, vibration may take place in otherdirections. In FIG. 3B, the second surface may be stationary or mayoptionally vibrate as shown by arrow 381. The vibrating of the surfacemay be initiated by mechanical means within the vibration richenvironment. For example, if the first surface is in an aircraft orautomobile, the vibrating of the surface may result from starting anengine. If for example, the surface is on a bridge, the vibration mayresult from natural means such as winds and/or water currents, or byother means such as the transportation of vehicles across the bridge.

Because of the manner in which the bimetallic strip 301 is secured asshown in FIGS. 3B and 3C, the strip undergoes mechanical stress due tothe vibration. Because the bimetallic strip comprises magnetostrictivematerials, the resulting mechanical stress rearranges the magneticmakeup of the strip, as well as the associated magnetic flux.

Step 350 is the inducing of an alternating current from the changingmagnetic flux. As shown in FIGS. 3B and 3C, a coil 375 a wrapped aroundthe bimetallic strip 301. An alternating current is induced in the coilas a result of the changing magnetic flux of the strip 301, which iscaused by the mechanical stresses and resulting alterations in thebimetallic strip. Although the coil 375 is shown in one orientation, thecoil may be positioned in other orientations to maximize the inductionof the current. At step 360, the induced current is stored via anelectrical storage element. Alternatively, the induced current may beconverted to another desired output using the appropriate circuitry. Theenergy harvesting method 300 is maximized by matching the bimetallicstrip components and dimensions to the vibration amplitude and stresscapability of the energy source.

A number of exemplary implementations have been described. Nevertheless,it will be understood that various modifications may be made. Forexample, suitable results may be achieved if the steps of describedtechniques are performed in a different order and/or if components in adescribed component, system, architecture, or devices are combined in adifferent manner and/or replaced or supplemented by other components.For example, the Fe-based alloy for use in the bimetallic strips, maynot necessarily be limited to Fe—Al or Fe—Ga, but other elements may beused for ease of alloy preparation, modification of device temperaturedependence, and other auxiliary effects. Accordingly, otherimplementations are within the scope of the following claims.

1. A bimetallic strip having only two layers, said bimetallic stripcomprising: a first substantially flat layer comprising a positivemagnetostrictive material; and a second substantially flat layerattached to the first substantially flat layer forming a dual layeredstrip, said second substantially flat layer comprising a flexiblematerial, wherein the first substantially flat layer comprises one of,an alloy of Fe and Al, wherein the alloy of Fe and Al comprisesFe_(100-x)Al_(x) wherein x is from about 5 to about 25, an alloy of Feand Ga, wherein the alloy of Fe and Ga comprises Fe_(100-y)Ga_(y)wherein y is from about 5 to about 35, and an alloy that is acombination of Fe_(100-x)Al_(x) wherein x is from about 5 to about 25,and Fe_(100-y)Ga_(y) wherein y is from about 5 to about 35, and whereinthe flexible material of said second substantially flat layer comprisesa negative magnetostrictive material or a permanent magnet.
 2. Thebimetallic strip of claim 1, wherein said first substantially flat layercomprises said alloy of Fe and Al and is provided in an alloy having asubstantial amount of said Fe_(100-x)Al_(x).
 3. The bimetallic strip ofclaim 1, wherein said first substantially flat layer comprises saidalloy of Fe and Ga and further comprises carbon.
 4. The bimetallic stripof claim 1, wherein said first substantially flat layer comprises saidalloy of Fe and Ga and is provided in an alloy having a substantialamount of said Fe_(100-y)Ga_(y).
 5. The bimetallic strip of claim 1,wherein said first substantially flat layer comprises said alloy of Feand Ga the flexible material of said second substantially flat layercomprises Ni or a permanent magnet, and wherein said first substantiallyflat layer further comprises C, Mn, S, Be, Sn, or a combination thereof.6. A bimetallic strip comprising: a first substantially flat layercomprising a positive magnetostrictive material; a second substantiallyflat layer attached to the first substantially flat layer forming a duallayered strip, said second substantially flat layer comprising aflexible material; and a third substantially flat layer attached to oneof said first substantially flat layer or said second substantially flatlayer, wherein said third substantially flat layer comprises a permanentmagnet, and wherein said first, said second, and said thirdsubstantially flat layers are attached so that there are no air gapswithin the bimetallic strip.
 7. The bimetallic strip of claim 6, whereinsaid second substantially flat layer comprises a negativemagnetostrictive material; and said first substantially flat layercomprises an Fe-based alloy, wherein said Fe-based alloy comprises;Fe_(100-x)Al_(x) wherein x is from about 5 to about 25, orFe_(100-y)Ga_(y) wherein y is from about 5 to about 35, or a combinationof said Fe_(100-x)Al_(x) and said Fe_(100-y)Ga_(y).
 8. The bimetallicstrip of claim 7 wherein, said Fe-based alloy is provided in an alloyhaving a substantial amount of said Fe-based alloy.
 9. The bimetallicstrip of claim 7, wherein said first substantially flat layer furthercomprises C, Mn, S, Be, Sn, or a combination thereof.
 10. The bimetallicstrip of claim 6, further comprising: a fourth substantially flat layerattached to one of said first substantially flat layer or said secondsubstantially flat layer, so that said first and second substantiallyflat layers are sandwiched between said third substantially flat layerand said fourth substantially flat layers, wherein said fourthsubstantially flat layer comprises a permanent magnet.
 11. Thebimetallic strip of claim 10 wherein, said second substantially flatlayer comprises a negative magnetostrictive material; and said firstsubstantially flat layer comprises an Fe-based alloy, wherein saidFe-based alloy comprises; Fe_(100-x)Al_(x) wherein x is from about 5 toabout 25, or Fe_(100-y)Ga_(y) wherein y is from about 5 to about 35, ora combination of said Fe_(100-x)Al_(x) and said Fe_(100-y)Ga_(y). 12.The bimetallic strip of claim 11 wherein, said Fe-based alloy isprovided in an alloy having a substantial amount of said Fe-based alloy.13. The bimetallic strip of claim 11, wherein said first substantiallyflat layer further comprises C, Mn, S, Be, Sn, or a combination thereof.14. A bimetallic strip comprising: a first substantially flat layercomprising a positive magnetostrictive material; a second substantiallyflat layer attached to the first substantially flat layer forming a duallayered strip, said second substantially flat layer comprising aflexible material; and a third substantially flat layer attached to thesecond substantially flat layer, so that said second substantially flatlayer is sandwiched between said first substantially flat layer and saidthird substantially flat layer, wherein said second substantially flatlayer comprises a permanent magnet, and said third substantially flatlayer comprises a flexible material, and wherein said first, saidsecond, and said third substantially flat layers are attached so thatthere are no air gaps within the bimetallic strip.
 15. The bimetallicstrip of claim 14, wherein said third substantially flat layer comprisesa negative magnetostrictive material; and said first substantially flatlayer comprises an Fe-based alloy, wherein said Fe-based alloycomprises; Fe_(100-x)Al_(x) x is from about 5 to about 25, orFe_(100-y)Ga_(y) wherein y is from about 5 to about 35, or a combinationof said Fe_(100-x)Al_(x) and said Fe_(100-y)Ga_(y).
 16. The bimetallicstrip of claim 15, wherein said Fe-based alloy is provided in an alloyhaving a substantial amount of said Fe-based alloy.